The invention relates to modular systems that include a rack assembly for inserting electrical printed circuit boards. Such rack assemblies include at least opposite cross-connecting bars made of electrically conductive material, which are covered with guide bars situated opposite each other in pairs. Such rack assemblies thus provide volume elements suited for the insertion of electrical printed circuit boards. Such volume elements are also called mounting sites and are normally arranged parallel side by side. Electrical printed circuit boards can be inserted into such volume elements, which are then also arranged parallel side by side.
FIG. 1 shows one possible basic standard construction of a rack assembly 1. The area for receiving printed circuit boards is bordered by cross-connecting bars made of electrically conductive material situated opposite each other. In the example shown in FIG. 1, there are two lower cross-connecting bars 5,7 and two opposite, upper cross-connecting bars 4,6. The cross-connecting bars 4,5 form the boundaries of the front side of the rack assembly 1, i.e., the insertion side 2 provided for positioning electrical printed circuit boards. The two cross-connecting bars 6,7 form the boundaries of the rear wall side 3 of the rack assembly 1, which can be separated by a rear wall conductor plate. The cross-connecting bars 4,5,6,7 can be mounted by their ends, e.g., inside a control cabinet. In FIG. 1 there are vertical side wall metal plates 8,9, to which the cross-connecting bars are screwed at their ends. Lastly, the upper and lower sides of the rack assembly 1 are closed by an upper and a lower cover plate 10,11.
So-called front elements are provided for closing the insertion side 2 of the rack assembly 1. Such front elements are assigned to the individual mounting sites on the interior of the rack assembly, to whose width they are adjusted and to which they can be connected or disconnected. This possibility of closure can be independent of whether or not the mounting site located behind a front element contains an electrical printed circuit board. Thus, empty mounting sites can be covered with a front element placed on the insertion side 2 of the rack assembly 1, in the manner of an empty site cover. Alternatively, electrical printed circuit boards can be provided with a front element on the front side, so that, after the printed circuit board has been inserted into the rack assembly 1, the front element covers the corresponding mounting site on the insertion side 2 in the same manner.
In FIG. 1, front elements 12,13 are provided for the two mounting sites 56,57 on the left side of the rack assembly 1. These front elements are multisectional in design. Thus, the front element 13 contains a vertical face plate 19 made of an electrically conductive material. The lower and upper front faces of the face plate 19 are provided with an end piece 20,21, which usually also consists of an electrically conductive material. As an example, these end pieces can be provided with so-called rotary lever pulling handles 22,23. Such handles can be operated by a person through a pivot action so that a front element 12,13 can be easily attached or taken off, or an electrical printed circuit board connected to a front element can be easily inserted or removed.
In the example shown in FIG. 1, the front element 12 has already been pushed on and completely covers the mounting site 56 located behind it, and lies in the plane of the insertion side 2 of the rack assembly 1. In this example, the front element 13 of the mounting site 57 situated behind it is affixed to the printed circuit board 59. This connection is advantageously achieved with the help of the two end pieces 20,21. The printed circuit board has for the most part already been inserted into the mounting site 57. After complete insertion into the mounting site 57, the front element 13 will come to lie flush against the front element 12 in the plane of the insertion side 2.
Guide bars for guiding the printed circuit boards are advantageously arranged in opposite pairs for each mounting site in the mounting zone between the cross-connecting bars. In the example shown in FIG. 1, the entire mounting zone between the upper and lower cross-connecting bars 4,6 and 5,7, i.e., the sum of all mounting sites, is already provided with such pairs of guide bars. Thus, the printed circuit board 59 is guided on the upper and lower front side by the guide bars 14,15 situated opposite one another.
When inserting front elements or units made of front elements and electrical printed circuit boards, such elements should be centered in the insertion direction, particularly immediately before the final inserted position is achieved. This prevents an accidental lateral shift of, in particular, the front elements, which could at least hinder complete insertion thereof. This centering is especially necessary if adjoining mounting sites are already covered with front elements.
Finally, it is preferable to form a secure electrically conductive contact between the front elements and the rack assembly, particularly if the front elements and their components largely consist of electrically conductive materials. Electrically conductive contacts may be classified into the following different types.
One first type of contact can be described as a protective contact or ground contact. Through such a contact, high stray currents can be diverted from front elements to the rack assembly and then interrupted by downstream network protection devices, e.g., load separating switches or stray current line protection switches, at a speed ensuring the protection of persons. A protective contact should be especially effective if all the printed circuit boards in a rack assembly are electrically activated.
Another type of contact is used for diverting electrostatic voltage and can be described as an ESD (electro static discharge) contact. In this way, static potentials can be diverted from front elements to the rack assembly and its ground connection. An ESD contact should be especially effective when printed circuit boards are inserted into or removed from a rack assembly.
European patent 0 579 859 B1 describes a printed circuit board with guide pins for exact positioning during insertion into a rack assembly. In that patent, two guide pins are provided for centering a printed circuit board on the outsides of the corner assembly bodies. These guide pins support a longitudinal guide bar on the side flanks of the opposite head during insertion. In addition, a ground contact pin is arranged between the guide pins. This ground contact pin drops into an encoding chamber containing a ground contact spring on the front side of the opposite head of the longitudinal guide bar when the printed circuit board is inserted.
The reference WO 96/42187 describes a front system for a printed circuit board with an active/passive switch. For centering, the end piece of the printed circuit board is provided with a guide pin designed to enter into a corresponding guide bore. In that reference, no elements are provided for producing a protective electrical contact between the front element and the cross-connecting bars.
The reference WO 97/49271 describes a rack assembly for electrical printed circuit boards. The printed circuit boards are provided on one longitudinal side with a contact strip designed as a conductor track, which is interconnected to a metallic face plate of the printed circuit board via an electric resistor.
When the printed circuit board is inserted into the rack assembly, the contact strip comes into an electrically conductive contact loop with a contact spring, which is integrated in a guide bar, particularly at the head area, and is connected to the corresponding cross-connecting bars in an electrically conductive manner. The face plate of the printed circuit board is also provided with a screw, through which a direct electrically conductive connection to the rack assembly is produced once the circuit board is in the inserted state, while circumventing the resistor. Implementations of guide bars with loop contact springs are known, e.g., from DE 36 24 883 and DE GM 295 09 185.
Lastly, DE 36 24 839 C2 describes a guide bar for printed circuit boards. Its guide groove is bordered by side walls, whereby one side wall is separated from the groove base in a section thereof, and is designed as a bell curve shaped plate spring in such a way that the width of the guide groove is tapered.
One object of the present invention is to provide a modular system with a rack assembly for inserting electrical printed circuit boards, which enables the simple subsequent installation of contact parts for protective contacts of front elements. Another object of the present invention is to provide an especially simple integration as well as simple subsequent installation of devices for redirecting static voltage potentials.
According to one formulation of the invention, these and other objects are solved by a modular system for electrical printed circuit boards having a rack assembly and electrically conductive front elements. The rack assembly is provided with mounting sites for insertion of the electrical printed circuit boards on a module side of the rack assembly, and includes opposite cross-connecting bars made of electrically conductive material, and guide bars for insertion of the printed circuit boards into the mounting sites. The guide bars are affixed to the cross-connecting bars and include fixing devices for insertion of locating contacts made of electrically conductive material, which are placed into low-ohmic contact on the cross-connecting bars and have respective contact zones. The electrically conductive front elements are each assigned to at least one of the mounting sites and each have at least one centering contact protruding in a direction of the module side of the rack assembly. When the front element is placed on the at least one mounting site, it comes into low-ohmic and high current-carrying contact with the contact zone of at least one of the locating contacts.
According to a further formulation of the invention, the modular system for electrical printed circuit boards includes, again, a rack assembly and electrically conductive front elements. The rack assembly is provided with mounting sites for insertion of the electrical printed circuit boards on a module side of the rack assembly. The rack assembly includes (i) opposite cross-connecting bars made of electrically conductive material, (ii) guide bars for insertion of the printed circuit boards into the mounting sites, wherein the guide bars include respective guide grooves and are affixed to the cross-connecting bars, and (iii) locating contacts made of electrically conductive material. These locating contacts are respectively assigned to the mounting sites, are placed into low-ohmic contact on said cross-connecting bars, have respective contact zones, and include respective contact blades that respectively extend into the guide grooves of the guide bars. Each of the electrically conductive front elements for the printed circuit boards include at least one centering contact protruding in a direction of the module side of the rack assembly. Upon insertion of the printed circuit board into the respective mounting site, the centering contact comes into low-ohmic, high current-carrying contact with the contact zone of a respective one of the locating contacts of the respective mounting site. In addition, the contact blades of the locating contacts respectively come into contact with the printed circuit boards to draw off electrostatic potentials.
According to yet another formulation, the invention provides a rack assembly including a guide bar, a receiving element and a front element. The guide bar supports a printed circuit board within the rack assembly. The receiving element is mounted to the guide bar, is composed of a different material than the guide bar, and has a contact cavity. The front element is fastened to the printed circuit board and includes a contact pin configured to mate with the contact cavity.